Gelatin has long been exploited as a binder in photographic elements wherein silver salts, dyes and other adjuvants are harbored therein. Gelatin is generally considered to be a protein comprising amino acid residues wherein an acid group of an amino acid is linked to a base group of another amino acid to form a polypeptide chain. The amino acid residues typically contain both amine and carboxylic acid moieties which are pendant or branching off of the main polypeptide chain. It is these pendant amines and carboxylic acid moieties which form the basis for many of the properties of gelatin.
For use in a photographic emulsion it is typically preferred to add gelatin and a hardening agent to an aqueous photographic emulsion prior to coating the emulsion on a support. Upon removal of water and other volatiles from the emulsion the peptide coupling or carboxyl activated hardening agent reacts to form bonds between the pendant amines and pendant carboxylic acid groups on the gelatin backbone. The hardening, known in the art as "instant" hardening or crosslinking, imparts a rigidity to the gelatin structure thereby protecting silver salts, dyes and adjuvants from migrating within the film structure. Gelatin is also advantageous in supplemental layers below or above the emulsion for abrasion protection, dye localization and the like.
Prior to displaying an exposed photographic element it is typically necessary to process the image either by heat or by chemicals as known in the art. Chemical processing involves introducing the photographic element to various chemicals which develop the image and remove excess silver salts, dyes and adjuvants. After chemical processing the photographic element is preferably dried thereby providing an image. The pendant carboxyls are detrimental to the drying process due to the propensity with which carboxyl groups absorb excessive water. Therefore it has long been desired in the art to block or more fully crosslink the gelatin carboxyls to provide a film element which can be dried more rapidly and thoroughly.
Yet another long felt need in the art is a means of decreasing the effect of static electricity generated as a photographic element traverses through various automatic processing machines. This has been accomplished by various techniques as known in the art all of which require either a supplemental layer with antistatic adjuvants or the use of various surfactants within the photographic emulsion. Auxiliary layers require an additional manufacturing step which is undesirable and surfactants within the photographic element are known to migrate and can affect the sensitometric performance of the film.
In recent years discrete layers in a photosensitive element containing co- or terpolymers with carboxyl and sulfonated comonomers have been claimed as providing superior antistatic protection. A significant shortcoming of these inventions is the excessive water absorption due to insufficient crosslinking of the carboxyl groups.